The exemplary embodiments relate to a display device and a projector (a projecting type of display device), which have a holding type of display mode and in which an image is formed by an optically modulating device, and an illumination device suitable for use in the display devices.
A related art holding type of optically modulating device, such as a liquid crystal panel, a liquid crystal light valve, a micro mirror array (DMD) and the like, controls a transmitted light amount or a reflected light amount per a unit of time to carry out optical strength modulation. In this type of device, the image is unclear in displaying a moving picture image. Especially in an edge part, the unclearness can be perceived to be a “blur.” KURITA TAIICHIRO, Display Method and Picture Quality in Displaying Moving Picture in Holding Type of Display, “Drafts of First LCD Forum” Liquid Crystal Society, August 1998, Pages 1 to 6 discloses investigations for addressing or solving the above problem, for example.
In order to enhance or improve quality of a moving picture in a liquid crystal display device, which is a holding type of display device, for example, the following options are considered to be effective.
(1) Enhancing or improving a liquid crystal material or contriving a driving circuit to enhance or improve a response speed of a display device; and (2) turning on an illumination device intermittently to achieve an impulse type of display mode.
At the moment, enhancement or improvement in quality of a moving picture in a liquid crystal device is progressing with respect to the enhancement or improvement of a liquid crystal material or contrivance of a driving circuit (option (1)). Such an approach, however, is not enough and enhancement or improvement of an illumination device or an illuminating method (option (2)) should also be examined. A discharge lamp widely used for a light source of a direct-viewing type of display device or a projecting type of display device (a projector) is not suitable for lighting a lamp intermittently. Accordingly, an optical system in which some device to control illumination light is provided in a path of illumination light to achieve intermittent illumination. In JP-A-2001-296841, for example, an illumination optical system is proposed in which illumination light in a narrow and long band shape (an illumination band) is generated in advance by way of an integrator optical system, and then, a mirror in the shape of a square pillar is rotated to scan with the band-shaped illumination light, and thereby, intermittently illuminate (scan-illuminate) a liquid crystal display device.